Bounce your tracks to the master track (recording) then copy the new master track to two (if stereo) new tracks. So now you have say tracks one and two with all the tracks you bounced onto them. And now you have another 6 tracks to record more stuff onto. Then repeat the bounce, copy tecnique. It is infinite in how many times you can do this process, but you might have to delete some of the tracks that you bounced to the master, to give more free tracks for recording.
Hope this is of any help or makes any sense atall, i am bad at explaining things like this!